This invention relates to electro-mechanical timing devices and more particularly to timers of the automatic reset type.
In many timing applications it is necessary to start and control the timer from a remote point and also have the time cycle adjustable. This has led to use of motor driven automatic reset timers in which a spring return timing mechanism resets to an adjustable starting position when a clutch is released. To start a timing cycle, the clutch is engaged and the mechanism drives to a "timed out" position in which one or more switches transfer from "timing" position to "timed out" position.
In some applications it is required to delay operation of the timer switch until the end of the time cycle. This is known as delay timing. In this case the timer switch is returned from timed-out to timing position prior to the start of the cycle so that no timer switch operation takes place at the start of the cycle.
In other applications it is necessary to energize a load at the start of the cycle and to deenergize it at the end of the cycle. This is known as interval timing. This type of operation requires more mechanism than simple delay timing, either built into the timer or a relay external to the timer.
In certain applications it is required or permissable for the timer to reset to starting position in response to a power interruption. Here the timer clutch is released in response to deenergization of an electromagnet. This is known as "on delay".
In other cases it is necessary for the timer to hold its position in case of power failure. In others it is required to reset in response to making of the control circuit. The timer clutch disengages in response to energization of the electromagnet. This is known as "off delay".
The different requirements met in the field in addition to the basic requirements of "on delay", "off delay", and "interval" are many. In some, the cycle start must be from closure of the control circuit, in others from control circuit opening. In some the control circuit action is only momentary. In others it is sustained. These various requirements have required numerous models of timers and in addition considerable outside circuitry to get the results needed.
In order to reduce models required and also reduce outside circuitry it has been common to build timers with two "delay" switches actuated by the timer and two "instantaneous" switches actuated by the electromagnet. These switches have individual terminals allowing the user to connect them in various manners to obtain different results from the timer. This is expensive. The customer must buy more than he needs. He must spend considerable time cross-wiring the switches. In addition, often half of the switches are used up cycling the timer so that they are not available for controlling external loads.
My copending application Ser. No. 333,767 filed Feb. 20, 1973, shows an automatic reset timer with multiple switches and with separate mode selectors for the switches and clutch at the back of the timer. This makes a single model of timer easily converted to give the results needed for the application and simplifies or eliminates external circuitry. This timer is in the expensive and high class field and its cost precludes its use in many applications not requiring this degree of quality.